Pumpless absorption refrigerator using a jet

ABSTRACT

An absorption refrigeration system using a two or more substance solution to achieve refrigeration that eliminates the need for a pump. The vapor pressure in a generator column is balanced by a pressure head of liquid solvent-solute solution. Re-dissolved solute is returned to the generator by causing some of the vapor to pass through a perforated tube or the like into the solvent where it is absorbed. At least some of the vapor is cooled to liquid solute and then expanded through an expansion valve into an evaporator to create a refrigerator. Hot vapor from the generator column can be passed through a jet to create a low pressure in the evaporator. No pump is necessary since the liquid is returned to the heating area of the generator by gravity. Closed loop control of the heating can optionally be achieved by using a pressure sensor in the rising generator column.

This application is related to and claims priority from U.S. Provisionalpatent application Ser. No. 60/902,132 filed Feb. 20, 2007. Application60/902,132 is hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to the field of absorptionrefrigerators and more particularly to an absorption refrigerator thateliminates the need for a pump.

2. Description of the Prior Art

A typical prior art absorption refrigeration system utilizes a solutionof two substances having different boiling points. Turning to FIG. 1, aschematic of a typical prior art system can be seen. A first containeracts as a generator or still where the liquid with the lower boilingpoint (the solute) is distilled from the liquid with the higher boilingpoint (the solvent) by the application of heat. The vapor of the solutethus produced passes to a condenser or condensing container where thevapor liquefies on cooling by exchanging heat with the externalatmosphere or a liquid shower like a water shower. The cooled liquid isthen permitted to evaporate through a restricted passageway into anevaporator having lower pressure. This process is endothermic and henceresults in refrigeration. The relatively low pressure of the evaporatorcontainer is due to absorption of the lower boiling point vapor or gasby higher boiling point solvent when the vapor passes into an absorbercontainer. The “rich” liquid produced in the absorber is then sent backto the generator for another cycle usually be a pump. Liquid from thegenerator container which has become “weak” due to the removal of thesolute is cooled and admitted to the absorber where it can absorb moresolute vapor or gas causing reduced pressure in the absorber. In manycases, additional heat exchangers and purifiers are added to improveefficiency. A very common practice is to use ammonia as the solute andwater as the solvent liquid. Like any binary solution, the boiling pointvaries with the relative concentrations of the two substances becominghigher as more ammonia leaves the solution. By putting solute back intothe solvent, the entire system can be operated in equilibrium at afairly constant temperature and pressure in the generator.

While the prior art refrigeration system described can perform quitewell in a number of circumstances, it requires a pump to return “rich”fluid from the absorber to the generator. This is because in the priorart system, the liquid needs to be transferred against a pressuregradient from the low pressure absorber to the high pressure generator.Where electricity is plentiful, this may not be a problem; however, forremote locations or portable use, it would be advantageous to have anabsorption refrigeration system that does need a pump.

SUMMARY OF THE INVENTION

The present invention relates to an absorption refrigeration systemusing a two-substance or binary solution to achieve refrigeration thatsuccessfully eliminates the need for a pump. This is a great advantagefor use in a location where there is little or no electricity, sinceabout half of the world's population lives without electricity. Thesystem still needs heat; however, this can be delivered by bottled gas,steam, or any other source of heat including burning wood or othersubstances. Providing heat is a relatively easy problem in the art,pumping a volatile liquid against a pressure gradient is a relativelydifficult problem, especially without electricity. The present inventionreplaces the pump by using a head of liquid to balance vapor pressure ina generator and a nozzle to help create a low pressure in andevaporator. The energy the pump would supply is supplied by gravity andby heat.

The vapor pressure in a generator column is balanced by pressure createdby a pressure head of liquid solvent. Re-dissolved solute is returned tothe generator by causing some of the vapor to pass through a perforatedtube or similar device into the solvent. At least some of the vapor iscooled to liquid and then expanded through an expansion valve to createa refrigerator. No pump is necessary since liquid is returned to theheating area of the generator by gravity.

DESCRIPTION OF THE FIGURES

Attention is now directed to several figures to help understand thepresent invention:

FIG. 1 shows a schematic diagram of a prior art system.

FIG. 2 shows a piping view of an embodiment of the present invention.Several drawings and illustrations have been provided to aid inunderstanding the present invention. The scope of the present inventionis not limited to what is shown in the figures.

DESCRIPTION OF THE INVENTION

The present invention relates to a liquid solvent absorptionrefrigerator that functions with no pump. An embodiment of the presentinvention is shown in FIG. 2 in the form of a piping diagram. It shouldbe noted that various solutions of different substances can be used inthe present invention. The most common and preferred solution is ammoniain water, so for further example in this description, ammonia and waterwill generally be used. Any solution of two or more substances withdifferent boiling points is within the scope of the present invention.

Ammonia is distilled from water as previously described in a generatorvessel 1 by the application of heat from a heat source 12. The vapor sogenerated pressurizes the vessel 1, and the riser column 2. Pressure ismaintained at a predetermined value by a pressure sensor 3 thattransmits a signal to the heat source 12 forming a control loop known inthe art. It is possible to construct the present invention without apressure sensor, since if the pressure gets too high, the liquid willpull away from the heating area. However, it is preferred to use asensor 3 to avoid fuel waste. A thermostatically operated valve 4 allowsor disallows gaseous ammonia to pass from the riser column 2 to anejector jet 5 depending on the temperature of the exit vapor from anevaporator 6 to be discussed. A check valve 7 prevents return of vaporto the evaporator when there is no flow through the ejector 5. When thethermostatically operated valve 4 is open, hot ammonia gas passes fromthe column 2 to the jet nozzle of the ejector 5 and through the venturior narrower part of the ejector 5 to the condenser 9 and perforated tube10 located in an absorber section 14. Heat exchange with thesurroundings lowers the temperature of the ammonia in the condenser 9liquefying it. Extended tubing in the absorber section 14 may be neededto remove heat from the ammonia gas since absorption generates some heatthat needs to be removed by exchange with the ambient. The liquidammonia gravitates to an expansion valve or orifice 8. The action of theejector 5 creates a low pressure in the evaporator 6 along with thelower pressure also created by the absorption process so that when theliquid ammonia passes through the expansion valve, it evaporates with anaccompanying drop in temperature. The rest of the ammonia gas thatenters the perforated tube 10 contacts the solvent in the verticalsection of the generator 14 and is there absorbed by the ammonia-watersolution in the generator tube.

As stated, ammonia flow through the ejector 5 produces a low pressure inthe evaporator 6 in accordance with the Bernoulli principle. Cooledammonia liquid passes through the expansion valve 8 where it expandschanging to a gaseous state. This free expansion takes place at almostconstant enthalpy and is well-known in the art of refrigeration to beendothermic. Hence the coils in the evaporator 6 cause the evaporatorspace 13 to become cold. The enclosed and insulated evaporator space 13becomes a refrigerator. It should be noted that additional ejectorspossibly combined with coolers could be arranged in series with theejector 5 to provide lower pressure in the evaporator 6 if desired orneeded. The expanded ammonia vapor then reenters the condenser 9 andabsorber 14 through the check valve 7 previously described.

Rich ammonia-water fluid is returned to the generator by the pressurehead H caused by the vertical nature of the piping. There is a balanceof pressure of the liquid in the descending part of the generator(pressure caused by the head H) against the pressure created by thevapor in the rising part of the generator 1. As previously stated, thiscan be controlled by the pressure sensor 3 at the top of the risinggenerator 1 which adjusts the heat input to the generator from the heatsource 12. As previously stated, the pressure sensor 3 is optional. Itis not possible to overpressure the generator because as pressureincreases beyond a particular amount, the liquid is pushed away from theheat source.

In some embodiments of the present invention, depending on thesubstances used and the vertical size, the pressure head H can be madesufficient so that 100% refrigerant such as ammonia can be used. In thisembodiment, the absorber with solute 14, 10 is not necessary and can beremoved by disconnected at points A, B and C in FIG. 2 and installing aconnection at the point marked D.

The over-all continuous operation is then that a solute is vaporized ina generator from a solution (or pure substance) by the application ofheat. The pressure in the generator is balanced against a pressure headof liquid in a descending section of the generator. The exact amount ofheat to maintain the pressure balance can be controlled by a pressuresensor that feeds back a signal to the heat source or can be simplyallowed to operate at a pressure equilibrium. The hot vapor is jettedand condensed in a condenser and then expanded through an expansionvalve into an evaporator to produce refrigeration in a closed, generallyinsulated, refrigerator space. Additional jetted vapor can be taken offand re-dissolved in the solvent in an absorber using a device like aperforated tube in the descending part of the generator. The jet causesa low pressure in an evaporator along with the pressure drop caused bythe absorption process. The pressure head of the liquid column dependson the height of the column from the base of the generator to the levelof the top of the solvent (where the perforated tube or other devicethat allows the vapor to dissolve in the solvent).

It should be noted that most of the solvent stays liquid constantlymaintaining the required pressure head. As is well-known in the art,whenever an binary solution is heated, the first vapor that leaves isalmost 100% pure solute. Without continuous refreshment of solute intothe solvent, the boiling point of the remaining solution graduallyincreases, and the vapor begins to contain more and more solvent. Thisis the case in the distillation of spirits. However, In the case of thepresent invention, the mixture is continuously refreshed with solutethat is re-dissolving in the solvent (at the perforated tube 10 in FIG.2). For this reason, the vapor produced in the rising generator column 2remains almost pure, and the boiling temperature remains constant.

While ammonia-water solutions have been used in examples, many otherbinary and other solutions can be used with the present invention. Theselection of solutions is governed mainly by the pressure needed tocondense at atmospheric temperatures and the heat transfercharacteristics, boiling points and toxicity of the liquids.Ammonia-water is preferred as one of the best possible solutions. It'sdisadvantage is toxicity. Water in lithium bromide can be used (and isnon-toxic). Here, water is the solute and refrigerant. However, waterboils at high temperatures compared to ammonia. This can lead to muchhigher operating temperatures and pressures. This can be overcome bymaintaining very low pressures in the system (on the order of about 2inches of mercury absolute in the condenser). This allows the system tooperate at much lower temperatures. Other possible solutions arealcohol-water, chlorine-water, HCl-water, and many others. Any solutionof two or more liquids, gasses or gas-liquids of different boilingpoints is within the scope of the present invention. Material used forpiping must be chosen based on the substances used in the mixture. Forexample, ammonia reacts with copper and hence copper piping cannot beused with ammonia. Other substances may react with other types ofpiping.

Several descriptions and illustrations have been presented to aid inunderstanding the present invention. One skilled in the art will realizethat numerous changes and variations are possible without departing fromthe spirit of the invention. Each of these changes and variations iswithin the scope of the present invention.

1. An absorption refrigerator not requiring a pump comprising: agenerator column with a rising portion and a descending portion, saidrising portion being heated and containing vapor; said descendingportion containing liquid, said liquid forming a pressure head in saiddescending portion, wherein said pressure head balances pressure of saidvapor in said rising portion; a jet attached to said rising portion ofsaid generator column, wherein said vapor is jetted through said jetcreating a low pressure in an evaporator, and wherein said vapor coolsand liquefies to form said liquid in said descending portion wherein atleast some of said liquid is passed through an expansion device intosaid evaporator creating a refrigerator.
 2. The absorption refrigeratorof claim 1 wherein said liquid is a solution of a solute in a solvent.3. The absorption refrigerator of claim 1 wherein said vapor is ammonia.4. The absorption refrigerator of claim 2 wherein said solvent is water.5. The absorption refrigerator of claim 2 wherein said solute isammonia.
 6. The absorption refrigerator of claim 2 further comprising anabsorption section where said solute re-dissolves in said solvent. 7.The absorption refrigerator of claim 6 wherein said absorption sectionincludes a perforated tube.
 8. The absorption refrigerator of claim 1further comprising closed loop control of pressure in said risingportion using a pressure sensor in said rising section controlling aheat source.
 9. An absorption refrigerator requiring no pump that uses asolution of a solute and a solvent, said solute having a boiling pointlower than that of said solvent comprising: a generator with a heatedvapor-containing portion and a liquid containing portion, saidliquid-containing portion forming a pressure head that balances pressurein said vapor-containing portion; a condenser in proximity to saidgenerator; an absorber in proximity to said condenser; an evaporator inproximity to said condenser; an ejector jet coupling said generator tosaid condenser, wherein vapor in said generator is jetted into saidcondenser causing a decrease in pressure in said evaporator, and whereina portion of said vapor enters said absorber and is re-dissolved in saidsolvent, said absorber being connected to said liquid-containing portionof said generator; and wherein another portion of said vapor condensesin said condenser forming a liquid that is passed through an expansiondevice into said evaporator causing a drop in temperature in saidevaporator, and wherein expanded gas passes from said evaporator intosaid condenser.
 10. The absorption refrigerator of claim 9 furthercomprising a check valve between said evaporator and said condenser thatprevents vapor from said condenser from entering said evaporator. 11.The absorption refrigerator of claim 9 further comprising a pressuresensor in said vapor-containing part of said generator.
 12. Theabsorption refrigerator of claim 11 wherein said pressure sensorcontrols a heater heating said generator.
 13. The absorptionrefrigerator of claim 9 wherein said absorber contains a perforatedtube.
 14. The absorption refrigerator of claim 9 wherein said solute isammonia.
 15. The absorption refrigerator of claim 9 wherein said solventis water.
 16. A method of absorption refrigeration comprising the stepsof: heating a solute-solvent solution causing said solute to boil offvapor into a rising portion of a generator column; jetting said vaporthrough a jet into a condenser, said jet causing a drop in pressure inan evaporator; condensing said solute to a liquid in said condenser;expanding said liquid solute through an expansion device into saidevaporator; allowing expanded solute vapor to re-enter said condenser;causing a portion of said vapor in said condenser to enter an absorberwhere it re-dissolves in a column of liquid solute-solvent solution,said column of solution in a descending portion of said generatorcolumn, and wherein said column of liquid forms a pressure head thatbalances pressure of said vapor in said rising portion of said generatorcolumn.
 17. The method of claim 16 wherein said solute is ammonia. 18.The method of claim 16 wherein said solvent is water.
 19. The method ofclaim 16 further comprising the step of controlling heating of saidgenerator using a pressure sensor in said rising portion of saidgenerator.
 20. The method of claim 16 further comprising using a checkvalve between said evaporator and said condenser to prevent solute vaporfrom entering said evaporator from said condenser.